When recovering hydrocarbons from subterranean formation containing particulate fines, such as silt sized or smaller particles, these particulates have a tendency to be displaced, for example, due to instability of the formation. Where a large volume of fluid is forced to flow through such a formation, the very fine particles (especially sand) may be transported to the surface and must then be disposed of. Disposal of large volumes of sand produced from unconsolidated or poorly consolidated formations presents serious problems in terms of the logistics of disposal. Erosion of downhole equipments such as tubulars, sandscreens, pumps, or valves owing to the high velocities of particulates, especially sand particles, can also occur. Repair or replacement of such equipment can only be carried out during period of shut-down in production. Fine particulates can also become lodged in the pores of the formation, in particular, the pore throats in an intergranular rock (the small pore space at the point where two grains of an intergranular formation meet, which connects two larger pore volumes). This at least partially plugs the pores of the formation thereby causing a reduction in permeability of the formation and hence a reduction in the rate of hydrocarbon production.
The production and movement of fine particulates, especially sand particles, is a major problem in the operation of hydrocarbon production wells, particularly those that penetrate unconsolidated formations. Loss of production may arise owing to plugging of gravel packs, sand screens, perforations, tubulars, surface flow lines or separators. In addition to damaging pumps or other downhole equipment, erosion of casing, tubulars, downhole equipment and equipment in surface facilities may also occur. This erosion can in some cases cause loss of a well owing to hole collapse or may require re-completion of the well (replacement of casing, tubulars and downhole equipment). Accordingly, there is a need for effective sand control.
US 2006/124303, for example, relates to a method of treating a subterranean formation which involves treating low quality particulates by providing to them coatings of first and second curable resins. Said particulates may then be injected into the subterranean formation where they are said to able to rebond and provide adequate consolidation strength for formation of a stationary, permeable particulate pack, such as a gravel pack.
Although gravel packs can provide some stabilisation for subterranean formations, there is a need for more direct chemical stabilisation of the fine particulate matter in the formation. For this purpose, chemical treatments have been proposed which involve strengthening a formation by injecting a chemical that bonds fine particulates together thereby preventing or reducing the production and movement of fine particles when the well is in production. However, such chemical treatments should avoid blocking the pores of the formation.
UK Patent number GB 2419614B, for example, describes a method for the treatment of a subterranean formation which contains sand particles, said method comprising contacting said formation with a material capable of increasing the residual matrix strength of said sand particles whereby to reduce or prevent their migration whilst said material, on contact with said formation effects a reduction in permeability of less than 40%, wherein said material comprises a compound of formula:(RO)3Si—(CH2)x-A-(CH2)y—Si(OR)3 wherein each R is independently a substituted or unsubstituted alkyl group having 1 to 18 carbon atoms, or a —COR group wherein R is as hereinbefore defined; A is an organic linking group or a group comprising an atom having a lone pair of electrons; x is 0 or a positive integer; and y is 0 or a positive integer. According to GB 2419614B bridging will, typically occur between surfaces of particles which are separated by up to 30 bond lengths, preferably 15-20 bonds lengths, e.g. on grain-to-grain contact. In this way, the residual matrix strength of the formation is increased. It is also said that the function of the group A is as a linking group and its precise chemical nature is of lesser importance provided this function is fulfilled. Generally, however it will comprise a chain 1 to 20 atoms long, preferably 1 to 10, especially 1 to 5. Thus, GB 2419614B teaches away from using polymeric linking groups. Also, although examples, of suitable linking groups are said to include both linear and branched alkylene chains which may be interrupted by heteroatoms such as nitrogen and oxygen, there is no specific disclosure of the use of either poly(oxyalkylenes) or polyurethanes as linking groups.